1. Field of the Invention
The present invention generally relates to an image recording and reproducing apparatus such as an AV (audio and/or video) server in which image data is recorded/reproduced by memory means which can be accessed randomly, and particularly to an image recording and reproducing apparatus and an image recording and reproducing method in which an image can be prevented from being disturbed due to digital errors caused in the normal tape speed playback mode and in which image data can be prevented from dropping out at the frame unit or the like in the high-speed playback mode.
2. Description of the Related Art
In recent years, recording/editing/transmitting systems in the broadcasting station are required to become able to simultaneously record a plurality of material data (video and/or audio data), to become able to edit material data which is being recorded in real time, and are also required to become able to transmit the same material data through a plurality of channels at the same time. To meet these demands, heretofore, there are used apparatus called an “AV (audio and/or video) server” or a “video server”.
An AV server generally includes a plurality of input/output (I/O) ports which can operate independently and a data memory section (e.g., hard disk drive (HDD)) which can be accessed randomly. When different material data are simultaneously inputted from these I/O ports to the AV server and recorded by the data memory section, it becomes possible to record a plurality of material data at the same time. When material data, which is being inputted from one I/O port and is being recorded, is simultaneously and parallelly reproduced from the data memory section and outputted from other I/O port, it becomes possible to edit the material data, which is being recorded, in real time in a nonlinear editing fashion. Furthermore, it becomes possible to simultaneously transmit the same material data through a plurality of channels by outputting the same material data reproduced from the data memory section from a plurality of I/O ports.
In the case of the nonlinear editing, in order to search an edit point whose time code is not clear, image data have to be reproduced at high speed (speed higher than a one-time normal speed) and the image data thus reproduced have to be displayed on a monitor, whereby a scene which serves an edit point can be detected
In the conventional AV server, when the edit point is searched at high speed, it is customary that image data are reproduced at random in the unit of frames. Specifically, when image data is reproduced in the twice normal speed playback mode, image data are reproduced on every other frame such as the first frame, the third frame, the fifth frame, . . . When image data is reproduced in the four-times normal speed playback mode, image data are reproduced on every three frames such as the first frame, the fifth frame, the ninth frame, . . .
However, when image data is reproduced at random in the unit of frames, image data of the skipped frame is lost completely. Accordingly, when it is intended to search a momentary scene in which a flash bulb is lit as an edit point, image data of the frame corresponding to such momentary scene is lost completely. As a result, it is frequently observed that such momentary scene cannot be detected.
To solve the above problem, the assignee of the present application has already proposed a system (so-called “G-shuttle system”) in which image data of individual frames can be prevented from dropping out completely in the high-speed playback mode (see Japanese patent application 11-317926).
FIG. 1 shows the manner in which image data are recorded by this G-shuttle system. Upon recording, inputted image data is divided in the unit of one frame to provide four image groups A, B, C and D, for example. Hard disk drives (HDDs), which are grouped as four groups W, X, Y and Z in response to the number of the image groups A, B, C and D, are adapted to record the image groups while a corresponding relationship between the image groups A, B, C, D and the groups W, X, Y, Z of the HDDs is being changed cyclically at every frame.
In the four-times normal speed playback mode of the high-speed playback modes, for example, ID (identification data) and image groups of the first 16 frames (frames No. 1 to No. 16 in FIG. 1) are reproduced from the group W, ID and image groups of the next 16 frames are reproduced from the group X, ID and image groups of the next 16 frames are reproduced from the group Y, and ID and image groups of the next 16 frames are further reproduced from the group Z of the HDDs 21 shown in FIG. 6 which will be described later on.
Then, image data of one frame is sequentially synthesized from image data (image groups A, B, C and D) of four consecutive frames in such a manner as to synthesize image data of first one frame from the image data (image groups A, B, C and D) of the frames Nos. 1, 2, 3 and 4 reproduced from the group W and to synthesize image data of the next one frame from the image data (image groups A, B, C and D) of the frames Nos. 5, 6, 7 and 8 reproduced from the group W. . .
With respect to image data of frames following 65th frame, the same processing is repeated for 64 frames.
As a result, there can be obtained image data containing one portion (one image group each) of each of image data of all recorded frames with the result that image data of individual frames can be prevented from completely dropping out. Accordingly, when the edit point is searched at high speed, if it is intended to search a momentary scene in which a flash bulb is lit as an edit point, then a part of image data of the frame corresponding to that momentary scene is displayed on the monitor, thereby making it possible for users to detect such momentary scene.
Also in the twice-normal speed playback mode and the eight-times normal speed playback mode, image groups are reproduced from the groups W, X, Y, Z over the range of the frames which are not identical to each other and image data of one frame is synthesized from the reproduced image groups A, B, C and D of the frames which are not identical to each other, whereby image data of individual frames can be prevented from completely dropping out (in the case of the eight-times normal speed playback mode, the number of frames in which image data completely drops out is decreased).
In the high-speed playback mode to search the edit point, even when an image on the monitor is disturbed due to a digital error existing in the image data reproduced from any of the HDD groups W, X, Y, Z, such disturbance of image, in particular, may not cause a serious problem.
On the other hand, upon broadcasting in which the recorded material data is reproduced in the normal speed mode (reproduced at one-time normal speed) and reproduced data is transmitted, an image displayed on a television receiver can be prevented from being disturbed due to this digital error.
However, there has not yet been disclosed an AV server in which the processing required in the high-speed playback mode can be simplified and in which an image can be prevented from being disturbed due to a digital error in the normal playback mode while the so-called G-Shuttle system is being used.